The invention generally relates to water purification, and more particularly to devices and methods for purifying water to a quality suitable for medical applications.
Various medical conditions require treatments that call for the injection of fluids into the human body. For example, severe trauma to the human body often involves significant loss of bodily fluids. Additionally, illnesses often cause diarrhea followed by dehydration and ion imbalance. In order to rehydrate the individual, injection of an intravenous saline or dextrose solution is required. Other medical applications (e.g., wound irrigation) require similar fluid purity levels.
An example of the need for injection of fluids into the body is in the area of dialysis. Treatments for patients having substantially impaired renal function, or kidney failure, are known as xe2x80x9cdialysis.xe2x80x9d Either blood dialysis (xe2x80x9chemodialysisxe2x80x9d) or peritoneal dialysis methods may be employed. Both methods essentially involve the removal of toxins from body fluids by diffusion of the toxins from the body fluids into a toxin free dialysis solution. Peritoneal dialysis can be performed without complex equipment and in a patient""s home. In the peritoneal dialysis process, the patient""s peritoneal cavity is filled with a dialysate solution. Dialysates are formulated with a high concentration of the dextrose, as compared to body fluids, resulting in an osmotic gradient within the peritoneal cavity. The effect of this gradient is to cause body fluids, including impurities, to pass through the peritoneal membrane and mix with the dialysate. By flushing the dialysate from the cavity, the impurities can be removed.
Due to indirect contact with bodily fluids through bodily tissues, rather than direct contact with blood, the dextrose concentration needs to be considerably higher in peritoneal dialysis than in hemodialysis, and the treatment is generally more prolonged. Peritoneal dialysis may be performed intermittently or continuously. In an intermittent peritoneal dialysis (IPD) procedure, the patient commonly receives two liters of dialysate at a time. For example, in a continuous ambulatory peritoneal dialysis (CAPD) procedure, the peritoneal cavity is filled with two liters of dialysate and the patient is the free to move about while diffusion carries toxins into the peritoneal cavity. After about 4-6 hours, the peritoneum is drained of toxified dialysate over the course of an hour. This process is repeated two to three times per day each day of the week. Continuous Cycle Peritoneal Dialysis (CCPD) in contrast, involves continuously feeding and flushing dialysate solution through the peritoneal cavity, typically as the patient sleeps.
Because peritoneal dialysates are administered directly into the patient""s body, it is important that the dialysis solution maintains the correct proportions and concentrations of reagents. Moreover, it is impractical to formulate and mix dialysis solutions on site at the typical location of administration, such as the patient""s home. Accordingly, peritoneal dialysates are typically delivered to the site of administration in pre-mixed solutions.
Unfortunately, dialysis solutions are not stable in solutions over time. For example, dextrose has a tendency to caramelize in solution over time, particularly in the concentrations required in the peritoneal dialysis context. To prevent such caramelization, peritoneal dialysis solutions are typically acidified, such as with hydrochloric acid, lactate or acetate, to a pH between 4.0 and 6.5. The ideal pH level for a peritoneal dialysate, however, is between 7.2 and 7.4. While achieving the desired goal of stabilizing dextrose in solution, the pH of acidified peritoneal dialysis solutions tends to damage the body""s natural membranes after extended periods of dialysis. Additionally, the use of acidified peritoneal dialysates tends to induce acidosis in the patient.
Bicarbonates introduce further instability to dialysis solutions. The most physiologically compatible buffer for a peritoneal dialysate is bicarbonate. Bicarbonate ions react undesirably with other reagents commonly included in dialysate solutions, such as calcium or magnesium in solution, precipitating out of solution as insoluble calcium carbonate or magnesium carbonate. These insolubles can form even when the reactants are in dry form. When occurring in solution, the reactions also alter the pH balance of the solution through the liberation of carbon dioxide (CO2). Even in the absence of calcium or magnesium salts, dissolved sodium bicarbonate can spontaneously decompose into sodium carbonate and CO2, undesirably lowering the solution""s pH level.
Accordingly, a need exists for improved methods and devices for formulating solutions for peritoneal dialysis. Desirably, such methods and devices should avoid the problems of non-physiologic solutions and incompatibility of dialysate reagents, and also simplify transportation, storage and mixing of such dialysates. One aspect of this problem is the need for mechanisms for safely and completely mixing constituents of dialysates in diluent at the point of administration. Another aspect of this problem is the need for producing injectable quality water or other diluent at the point of administration.
It is often advantageous to provide purified fluid independently of other constituents in the injected fluid. In many situations, independent provision of purified water simplifies transport and storage of solution constituents. In the case of peritoneal dialysis, preparing dialysate solution from dry reagents and independently provided pure water also minimizes the time for which unstable solutions must be stored prior to administration. Similarly, many other unstable solutions should be prepared soon before administration, preferably at the site of administration.
On site purification of fluids is also advantageous in a number of other medical applications, including intravenous injection, intramuscular injection, orally administered fluids, wound irrigation, use in instrument cleaning solutions, and general employment by immuno-compromised individuals (e.g., AIDS patients, geriatrics, etc.).
While separating provision of injectable quality fluid from other constituents can simplify transportation and delay production of unstable solutions, transporting purified water to the site of administration, even if produced and shipped separately from dry reagents, can represent considerable costs, as well as introducing opportunities for contamination. Transportation costs and contamination are particularly problematic when fluids are to be administered outside of a controlled hospital or clinic environment. Problems are even further exacerbated in lesser-developed countries, such as in the Indian subcontinent and Africa. Even in a hospital setting, the ability to convert available water into injectable quality water on site can reduce transportation and storage costs as well as avoiding the risk of contamination during transportation and storage.
Therefore, a need exists for a method and apparatus that allow preparation of injectable quality fluid from available fluid. Desirably, the apparatus should be transportable and convenient for on-site use in remote locations.
In satisfying the aforementioned needs, the embodiments described herein provide a portable apparatus and method for purifying fluid to levels suitable for medical applications, including injection into the human body.
In accordance with one aspect of the present invention, a portable apparatus is provided for producing injectable quality fluid. The apparatus includes a housing that defines a fluid flow path from an inlet port to an outlet port. A depth filtration stage, an organic filtration component, a deionization resin bed and a permeable membrane are held within the housing along the fluid flow path. The permeable membrane has a porosity of less than about 0.5 xcexcm and is configured to retain endotoxins.
In accordance with another aspect of the present invention, a water purification pack for producing injectable quality water includes a container. The container defines a flow-through path from an inlet to an outlet with an average cross-sectional area of less than about 20 square inches. The container houses purification elements within the path, including a permeable membrane having a porosity of no more than about 0.5 xcexcm. The purification elements provides a back-pressure low enough to allow fluid flow greater than about 30 mL/min under a feed pressure of between about 5 psi and 10 psi.
In accordance with another aspect of the invention, a method is provided for producing injectable quality of water. The method includes providing a portable purification pack with a housing surrounding purification elements in series. Non-sterile water is provided to an inlet of the housing under a feed pressure of less than about 20 psi. The water passes through the purification elements. Purified water exits from an outlet of the housing. The purified water has an organic content, conductivity, pH level and particulate contamination level suitable for injection into the human body.
In accordance with another aspect of the invention, a method is provided for producing fluid for medical applications. The method includes providing a portable housing. Non-sterile fluid passes through the housing. Particulate contamination, organic matter, dissociated ions, microbes and endotoxins from the feed fluid are retained within purification elements in the housing. Fluid suitable for medical applications is then output from the housing.